From nobody Sun Feb 8 19:55:01 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 81626C77B61 for ; Sat, 8 Apr 2023 12:27:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231305AbjDHM1e (ORCPT ); Sat, 8 Apr 2023 08:27:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231302AbjDHM1H (ORCPT ); Sat, 8 Apr 2023 08:27:07 -0400 Received: from mail-40133.protonmail.ch (mail-40133.protonmail.ch [185.70.40.133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4D55113D3 for ; Sat, 8 Apr 2023 05:26:44 -0700 (PDT) Date: Sat, 08 Apr 2023 12:26:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=protonmail3; t=1680956797; x=1681215997; bh=YjWJqyzY7rAxB/8T748G6J4lTdaIt8uzOIDk7TzSA8o=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: Feedback-ID:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID:BIMI-Selector; b=yJI2kW0bjVdmWEnbNqeuak4+eblElCb6I+DrB69qGiFObCyFe0TNVXjzucDlFNfcK 3bupOg9//vx2vp7dkOSCF/7fSzWBPsZ6rM0VjUUWWqwgg13oNwCa0BPDHmwfDRcAM1 v7j1UjxhQC+1Bhd/tolmiWccVVkd5w8EfZucU5lUATEn29hvrg/wxMfs1xxmIbjcL9 7NDlY7T9dbpyw2VtJf9MIwzk6OrFWsJIAE1ohjuam3cgORImgEicR5MQjUBIKwLUQO 7fMRssbNsGuEAuaium3EN9Put5zzj7l/cq0v+MDqWGwKa2Kmzr/itMLg2LJhzRXouk fnINbVCzhYZjg== To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Alice Ryhl , Andreas Hindborg From: Benno Lossin Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev, Benno Lossin , Alice Ryhl , Andreas Hindborg Subject: [PATCH v7 14/15] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` Message-ID: <20230408122429.1103522-15-y86-dev@protonmail.com> In-Reply-To: <20230408122429.1103522-1-y86-dev@protonmail.com> References: <20230408122429.1103522-1-y86-dev@protonmail.com> Feedback-ID: 40624463:user:proton MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" `UniqueArc::try_new_uninit` calls `Arc::try_new(MaybeUninit::uninit())`. This results in the uninitialized memory being placed on the stack, which may be arbitrarily large due to the generic `T` and thus could cause a stack overflow for large types. Change the implementation to use the pin-init API which enables in-place initialization. In particular it avoids having to first construct and then move the uninitialized memory from the stack into the final location. Signed-off-by: Benno Lossin Reviewed-by: Alice Ryhl Reviewed-by: Gary Guo Reviewed-by: Andreas Hindborg --- rust/kernel/lib.rs | 1 - rust/kernel/sync/arc.rs | 16 +++++++++++++--- 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 821bd067151c..2d7606135ef6 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -28,7 +28,6 @@ #[cfg(not(CONFIG_RUST))] compile_error!("Missing kernel configuration for conditional compilation"); -#[allow(unused_extern_crates)] // Allow proc-macros to refer to `::kernel` inside the `kernel` crate (thi= s crate). extern crate self as kernel; diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 43a53fbe175d..d05caa723718 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -18,7 +18,8 @@ use crate::{ bindings, error::{self, Error}, - init::{InPlaceInit, Init, PinInit}, + init::{self, InPlaceInit, Init, PinInit}, + try_init, types::{ForeignOwnable, Opaque}, }; use alloc::boxed::Box; @@ -30,6 +31,7 @@ use core::{ pin::Pin, ptr::NonNull, }; +use macros::pin_data; /// A reference-counted pointer to an instance of `T`. /// @@ -122,6 +124,7 @@ pub struct Arc { _p: PhantomData>, } +#[pin_data] #[repr(C)] struct ArcInner { refcount: Opaque, @@ -502,9 +505,16 @@ impl UniqueArc { /// Tries to allocate a new [`UniqueArc`] instance whose contents are = not initialised yet. pub fn try_new_uninit() -> Result>, AllocErro= r> { - Ok(UniqueArc::> { + // INVARIANT: The refcount is initialised to a non-zero value. + let inner =3D Box::try_init::(try_init!(ArcInner { + // SAFETY: There are no safety requirements for this FFI call. + refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }), + data <- init::uninit::(), + }? AllocError))?; + Ok(UniqueArc { // INVARIANT: The newly-created object has a ref-count of 1. - inner: Arc::try_new(MaybeUninit::uninit())?, + // SAFETY: The pointer from the `Box` is valid. + inner: unsafe { Arc::from_inner(Box::leak(inner).into()) }, }) } } -- 2.39.2